This invention relates to an image processing apparatus and method for inputting and encoding a fundus image.
Medical images used in patient examination and the like can now be handled as digital data. In order to archive efficiently large quantities of medical image data generated daily, the usual practice at many clinical locations is to put the image data into electronic form, compress and store it. In view of this tendency, compression schemes suited to medical images are being studied. For example, a multilevel reversible compression method such as JPEG-LS is known as a method of compression suited to medical images.
However, in special images such as an image of the fundus of the eye, reversible compression is not necessarily appropriate in certain cases. The reason for this is that since a fundus image is one in which the region photographed, namely the fundus of the eye under examination, is stationary, an imbalance appears in the color characteristic of the subject and color information is not dispersed uniformly in each of the R, G, B color components of the recorded digital image. Accordingly, color planes that contain a great deal of unnecessary information are also contained in this information. In view of the increasing number of photographs of such medical images, it would be helpful if even a few more images could be stored on an effective recording medium without sacrificing information that is vital for analysis. This can be achieved by not storing the image information of all color components.
With the conventional reversible compression scheme mentioned above, it is customary for the image data of one screen to be compressed at the same resolution. However, this is not necessarily appropriate for a special image such as a fundus image. The reason for this is that a fundus image contains important regions that are essential for diagnosis, one such region being the optic nerve head. The head of an optic nerve is a portion of interest when judging the progress of a glaucoma, which is a typical eye disease, and it is necessary to closely scrutinize the condition of the capillary vessels by checking the state of travel of the capillary vessels in the interior of this region. When a diagnosis is made on the basis of the capillaries, a key point is the extent to which fine blood vessels can be observed and discovered because this can lead to early discovery and treatment of diseases.
Accordingly, although the original data must not be lost at the time of image compression with regard to image information corresponding to important regions of the kind described above, in other regions it will suffice to merely ascertain the state of intersection or meander of blood vessels that have at least a certain diameter; these regions do not require a high-resolution image. This means that by storing important regions of a fundus image and regions that are not so important upon compressing them at different compression rates, the image can be compressed at a higher compression rate overall so that the amount of encoded image data stored can be reduced.
An object of the present invention is to provide an image processing apparatus and method through which a designated region of an image can be encoded at a low compression rate and other regions at a high compression rate to thereby raise the encoding efficiency of the image as a whole.
Another object of the present invention is to provide an image processing apparatus and method in which a first color component of a designated region of an image can be encoded at a low compression rate and other color components at a high compression rate to thereby raise the encoding efficiency of the image as a whole.
According to the present invention, the foregoing object is attained by providing an image processing apparatus for encoding image information, comprising: input means for inputting image information of a plurality of color components; designation means for designating a prescribed region in the image information; and encoding means for encoding a first color component included in a plurality of color components of the prescribed region designated by the designation means, and encoding a second color component, which is included in the plurality of color components, and the first color component other than in the prescribed region at a compression rate higher than that of the first color component of the prescribed region.
Further, according to the present invention, the foregoing object is attained by providing an image processing met hod for encoding image information, comprising: an input step of inputting image information of a plurality of color components; a designation step of designating a prescribed region in the image information; and an encoding step of encoding a first color component included in a plurality of color components of the prescribed region designated at the designation step, and encoding a second color component, which is included in the plurality of color components, and the first color component other than in the prescribed region at a compression rate higher than that of the first color component of the prescribed region.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.